cosmetic: s/BOARD_LATE_INIT/CONFIG_BOARD_LATE_INIT

This renames BOARD_LATE_INIT to CONFIG_BOARD_LATE_INIT.
Along the way it removes some leftover

 #define BOARD_LATE_INIT		1

and adds some basic documentation for board specific
callbacks in README.

Signed-off-by: Helmut Raiger <helmut.raiger@hale.at>
Acked-by: Stefano Babic <sbabic@denx.de>
diff --git a/include/configs/xaeniax.h b/include/configs/xaeniax.h
index 8a41416..6dce8ae 100644
--- a/include/configs/xaeniax.h
+++ b/include/configs/xaeniax.h
@@ -45,7 +45,7 @@
 #define	CONFIG_SYS_TEXT_BASE	0x0
 
 
-#define BOARD_LATE_INIT		1
+#define CONFIG_BOARD_LATE_INIT
 
 
 #undef CONFIG_USE_IRQ			/* we don't need IRQ/FIQ stuff */